1. Field of the Invention
The present invention relates to an artificial-photosynthesis module that receives light to electrolyze water and decompose the water into hydrogen and oxygen, using photoelectric conversion elements, and particularly, an artificial-photosynthesis module that can adjust a voltage required for electrolysis of water.
2. Description of the Related Art
In the related art, as one form of using solar light energy that is a renewable energy, there is suggested a hydrogen manufacturing apparatus that utilizes electrons and positive holes obtained by photoelectric conversion for a decomposition reaction of water, using a photoelectric conversion material used for solar batteries, and thereby manufactures hydrogen used for fuel cells or the like (for example, refer to JP2004-197167A).
In the hydrogen manufacturing apparatus disclosed in JP2004-197167A, a photoelectric conversion part or a solar battery in which two or more pn junctions that generate an electromotive force if solar light enters are connected in series is provided, an electrolytic solution chamber is provided on a lower side of the photoelectric conversion part or the solar battery opposite to a light-receiving surface that receives solar light on an upper side of the photoelectric conversion part or the solar battery, the inside of an electrolytic chamber is divided by the ion-conducting partition wall or a diaphragm, and water is electrolyzed and hydrogen is generated by the electrical energy generated in the photoelectric conversion part or the solar battery by receiving solar light.
In JP2004-197167A, a GaAs solar battery with an electromotive force of 0.9 V and a GaAs solar battery with an electromotive force of 1.7 V are used, the values of currents to be generated are equal, and the sum of the electromotive forces is made equal to or higher than a practical electrolysis start voltage, that is, equal to or higher than a voltage required for electrolysis of water.
Additionally, in JP2004-197167A, water is electrolyzed by using electrode plates connected to p-type and n-type semiconductors of the solar battery as an anode and a cathode, respectively. Thus, the conversion efficiency from solar energy to hydrogen can be made high.